一种配网单相接地选线的频带自适应获取方法

小电流接地系统单相故障选线中,目前频带的选择方法中被广泛采用的是首容性频带方法,但是这种方法易受配网运行方式、线路参数不精确等因素的影响。为了克服以上缺点,提出一种基于矩阵束算法的配电网单相接地选线频带自适应获取方法。频带下限在不接地系统中为0,经消弧线圈接地为150 Hz;频带上限的确定方法为首先通过矩阵束算法提取各出线零序电流的共有频率以及对应的相位,然后找到满足相位关系的最大频率,此最大频率就是频带的上限。PSCAD仿真和故障录波验证了该方法在各种故障情况下的有效性。此方法有望提高小电流接地系统单相接地故障时的选线正确率。     

高强抗震钢筋的研究现状

基于高强抗震钢筋的基本特征,介绍了微合金化、余热处理及细晶化技术在生产高强抗震钢筋中的应用。微合金化技术相对于其他两种应用更为广泛,余热处理和细晶化技术比微合金化成本低,无需添加合金元素,且能满足钢筋的抗震性能。通过对3种工艺的综合分析,提出在生产高强抗震钢筋时,应当将微合金化与余热处理结合起来,这样不仅节约生产成本,还有利于提高钢筋的抗震性能。     

Polyhydroxyalkanoate‐based drug delivery systems

Microbial polyhydroxyalkanoates (PHAs) have been a subject of significant research interest in the past few decades. The recent development of novel functionalized PHAs has opened up new possibilities to combine the good biocompatibility of PHA‐based drug delivery systems to, for example, improve drug loading and release properties, targeting or imaging functionalities. This mini‐review presents some recent scientific developments in the preparation of functionalized PHAs, PHA–drug and PHA–protein conjugates, multifunctional PHA nanoparticles and micelles as well as biosynthetic PHA particles for drug delivery. These developments in combination with the generally excellent biocompatibility of PHA materials are expected to further expand the interest in PHA materials for drug delivery and other therapeutic applications. © 2016 Society of Chemical Industry     

NiO/Al_2O_3基催化剂的TPR特性研究

NiO/Al_2O_3基催化剂用于替代贵金属催化剂,被广泛应用于石油和石化领域生产过程的加氢、脱硫和脱氮。采用TPR方法,研究不同Ni含量NiO/Al_2O_3及不同载体的催化剂还原特性。结果表明,NiO/Al_2O_3催化剂在10%H_2-Ar气氛下,还原温度范围较宽,为(300~800)℃,其中,(500~600)℃还原速率最大;随着NiO含量的增加,起始还原温度降低,还原耗氢量按比例增加;以MgO为载体的NiO催化剂还原呈现双峰特征,以SiO2和TiO2为载体的NiO催化剂的初始还原温度比NiO/Al_2O_3催化剂降低(100~200)℃。     

Thermoset lactic acid‐based resin as a matrix for flax fibers

Thermoset composites were produced from flax fibers and a novel lactic acid (LA)‐based thermoset resin. This resin is based on methacrylated, star‐shaped oligomers of LA. The main purpose of this work was to evaluate whether this resin can be used to produce structural composites from flax fibers. Composites were prepared by spray impregnation followed by compression molding at elevated temperature. The tests showed that composites can be produced with as much as 70 wt% fiber. The composites were evaluated by tensile testing, flexural testing, charpy impact test, dynamic mechanical thermal analysis (DMTA), and low‐vacuum scanning electron microscopy. The ageing properties in high humid conditions were evaluated, the Young's modulus ranged from 3 GPa to 9 GPa in the best case. This work shows that structural composites can be produced from renewable material. It is clear from the results that these composites have properties that make them suitable for furniture, panels, or automotive parts. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ca2-xSmxCo2O5热电材料的制备及性能

采用溶胶-凝胶法,以柠檬酸为络合剂、乙二醇为分散剂、硝酸盐为原料制备Sm3+掺杂Ca2-xSmxCo2O5粉末。前驱粉体经过常压烧结制备块体材料,在室温至600℃,研究样品的电阻率ρ、Seebeck系数S和功率因子P。结果表明:Sm3+摩尔掺量x=0.10～0.30时,与标准PDF 37-0668对比,所有X射线衍射峰一致且没有偏移;当x=0.45时,出现Sm3+的杂质衍射峰。Sm3+掺杂对材料的热电性能有较大的提高,在很大程度上降低材料的ρ、提高S,当x=0.30时,样品的电学性能最佳,在600℃时P达到最大,为1.25×10-4 W/(m.K2)。     

航天紧固件用TC4钛合金棒材固溶时效后的组织与性能

对航天用紧固件TC4钛合金棒材进行固溶时效处理,对棒材不同位置进行显微组织观察、硬度和室温拉伸性能检测。结果表明:TC4钛合金棒材经固溶时效后表面至心部的组织与性能受冷却速度的影响呈现显著差异。固溶时效后的显微组织由稳定的等轴α相、弥散的马氏体α′相和亚稳定β相组成,试样端面上因冷却速度相差不大,次生α相的形态和含量没有明显差异;中部截面上边部至心部的次生α相含量逐渐增多,同时次生α相片层厚度逐渐增大并趋于等轴化。端面上不同位置显微硬度值没有明显差异,但中部截面上由边部至心部的显微硬度值呈总体降低趋势,且中部截面上边部的显微硬度值与端面相差不大。试样心部因固溶过程中冷却缓慢,整体试样的室温拉伸性能明显低于去除心部的试样。     

Sorption of Pb(II), Cr(III), Cu(II), As(III) to peat,and utilization of the sorption properties in industrial waste landfill hydraulic barrier layers

The low conductivity landfill barrier layers protect the groundwater and soil by limiting the water flow through the bottom layers of the landfill material. Many materials used in hydraulic barrier layers also have sorption properties which could be used to reduce environmental risks. The adsorption of lead, chromium, copper, and arsenic to peat was studied with a batch-type test and a column test for compacted peat, both without pH adjustment in acidic conditions. Peat adsorbed all the metals well, 40 000 mg/kg of lead, 13 000 mg/kg of chromium, and 8400 mg/kg of copper in the column test. Arsenic was only tested in a batch-type test, and in that peat adsorbed 60 mg/kg of arsenic. The column test showed heavy metals to be adsorbed on the surface layers of the compacted peat sample, on the first centimeter of the sample. The adsorption was much greater in the column test than in the batch-type test, partly due to the different pH conditions and the buffer capacity of the peat in the column test. The liquid/solid ratio of the column experiment represented a time period of approximately 40 years in a landfill, under Finnish climate conditions. The hydraulic conductivity of the peat decreased as it was compressed, but it already met the hydraulic conductivity limits set by European Union legislation for the hydraulic barrier layer (1 × 10⁻⁹ m/s at a pressure of 150 kPa for a 5-m layer), with a pressure of 50 kPa. The results show that peat would be an excellent material to construct compacted, low hydraulic conductivity layers with adsorption properties in, e.g. industrial waste landfills.     

An analysis of students’ spontaneous computer-mediated help seeking: A step toward the design of ecologically valid supporting tools

This study analyzes middle school students’ spontaneous mathematics-related help-seeking behavior, in view of making ecologically valid recommendations for the design of supporting tools or “help systems”. Our aim was to investigate the content of students’ help-seeking messages – Are there different forms of help-seeking messages and do they evolve with age? We used the archives of a French forum that provides students with free individualized help in mathematics. The data consisted of 206 messages sent by French middle school students over a period of 42 months. The constituent categories of the messages were identified. The results showed that not all middle school students use the same help-seeking “format”. Compared to sixth graders, ninth graders wrote messages containing more constituent categories, i.e., they provided the online expert with more kinds of information. A detailed analysis of the categories further showed that older students’ messages more often contained explicit help requests and contextual information than did younger students’ messages. Thus, the messages of the oldest students (age 15) were both cognitively more understandable and socially more acceptable than those of the youngest students (age 11). The interpretation of these findings and their implications for designing help systems are discussed.